I'll take you out with me on track and we'll see what you say then about the MC box and how nimble it is. It's not that heavy a car really when you consider they fit similar boxes to M5, RS6 etc...
Done plenty of track driving in my time, much of it in much lighter cars. I would take a 160bhp Caterham any time over any of the fat 450-550bhp cars. Sure you can mask the issue by going to high average speed circuits but on more technical circuits - like Knockhill - these heavy cars are all over the place, largely due to the inability of the brakes to keep up.
None of the above is gearbox related, purely weight.